and setting up the notification to send the email to the assigned users:

Another extension is that the comma separated email address lists, as a result of Formula-E-mail calculations, are allowed in the notifications as well. If you are producing the list of e-mails via summary's Concatenate function, simply wrap the result into the Formula-E-mail column to allow hyperlinking.

After that you are able to use the Formula-E-mail column in the notifications.

All of the above obviously apply to the email alerts sent from the workflow rules.